1. Field of the Invention
The present invention relates to a process for producing chloroprene. More particularly, it relates to a process for producing chloroprene by reacting 3,4-dichlorobutene-1 in an aqueous solution of an alkali metal hydroxide to result a dehydrochlorination.
2. Description of the Prior Arts
Chloroprene can be produced by chlorinating excess of butadiene to prepare a reaction mixture containing 3,4-dichlorobutene-1 and 1,4-dichlorobutene-2 and separating the unreacted butadiene and isomerizing 1,4-dichlorobutene-2 to 3,4-dichlorobutene-1 and converting 3,4-dichlorobutene-1 to chloroprene by reacting 3,4-dichlorobutene-1 in an aqueous solution of a base to result a dehydrochlorination. However, 1-chlorobutadiene-1,3 is usually formed as a by-product in the dehydrochlorination.
It has been well-known to result a dehydrochlorination of 3,4-dichlorobutene-1 in an aqueous solution of a base. The chloroprene obtained by such conventional process, usually contains 2 to 3 wt.% of 1-chlorobutadiene-1,3. Accordingly, it has been known that physical properties of the polymer produced by using such chloroprene containing 1-chlorobutadiene-1,3 are inferior.
As well-known, boiling points of chloroprene and 1-chlorobutadiene-1,3 at the atmospheric pressure are respectively 59.4.degree. C. and 68.4.degree. C. In order to separate them, highly precision distillation is required. Moreover, a residence time of chloroprene in a precision distillation tower is long so as to cause easily a popcorn polymerization of chloroprene during the distillation step whereby it is difficult to obtain chloroprene having high purity in an industrial process.
In order to overcome such disadvantages, it has been proposed to add an organic solvent to the aqueous solution of a base. However, a satisfactory result could not be obtained.
For example, in Japanese Examined Patent Publication No. 25054/1967, ethyl alcohol is added in the reaction at 70.degree. C. whereby about 1% of 1-chlorobutadiene-1,3 is formed as the by-product. In Japanese Unexamined Patent Publication No. 106907/1975, propanol-2 is added in the reaction at 71.degree. C., whereby 1.2% of 1-chlorobutadiene-1,3 is formed as the by-product. In Japanese Examined Patent Publication No. 20283/1970, dimethylsulfoxide is added in the reaction and there is no description of 1-chlorobutadiene-1,3. In U.S. Pat. No. 3,079,446, an ether alcohol or a water soluble cyclic ether is added in the reaction. However high reaction temperature such as 80.degree. to 120.degree. C. is required whereby it is considered to form relatively large amounts of the polymer and 1-chlorobutadiene-1,3 as the by-product.